1. Technical Field
The present invention relates to a discharge lamp driver, a light source, a projector, and a method of driving a discharge lamp.
2. Related Art
Discharge lamps including high-pressure mercury lamps used for projectors or the like emit light by arc discharge within gases in plasma state. The arc discharge produces various reactions within the discharge lamp and causes illuminance reduction of the discharge lamp. There is a task of suppressing the illuminance reduction of the discharge lamp and extending the life of the discharge lamp.
Generally, as causes of the illuminance reduction of the discharge lamp, three main causes of blackening that electrode materials evaporated by arc discharge attach to the inner wall of the arc tube of the discharge lamp, devitrification that the inner wall of the arc tube is crystallized to be opaque due to its higher temperature and transmittance is lower, and electrode wear due to arc discharge are known.
As a method of suppressing the electrode wear, a method of controlling a distance between electrodes by controlling an amount of power supplied to the discharge lamp and suppressing excessive melt of the electrodes has been disclosed (for example, Patent Document 1 (JP-A-2010-114064)).
Further, as a method of suppressing blackening and devitrification, a method of effectively suppressing blackening and devitrification by steadily using a drive current having a larger frequency than 1000 Hz has been disclosed because it is known that an alternating current having a high frequency is effectively used as the drive current (for example, Patent Document 2 (JP-A-2012-243681)).
However, for example, in the method disclosed in Patent Document 1, the evaporated electrode material may attach to the inner wall of the arc tube and blacken. In this case, the electrode material attaching to the inner wall of the arc tube raise the temperature of the inner wall of the arc tube and devitrification is likely to occur.
Further, for example, in the method disclosed in Patent Document 2, the high frequency is used as the drive current, the temperature variations of the electrodes decrease and the electrodes are likely to be worn in a short period.
Accordingly, for example, in application to a projector, in order to improve use efficiency of light, it is preferable to maintain the smaller distance between electrodes and reduce the magnitude of light emission, however, for suppression of electrode wear, suppression of blackening and devitrification is difficult and, for suppression of blackening and devitrification, suppression of electrode wear is difficult. Therefore, it has been difficult to achieve a good balance between the suppression of blackening and devitrification and the suppression of electrode wear and extend the life of the discharge lamp.